With the great development of public traffic construction, underground passages and elevated highways constructed in the downtown area of city are getting more and more for improving the space utilizing efficiency. Although the traffic constructions is capable of improving the space utilization or transportation efficiency, those constructions could become obstructions for impeding the reception of satellite signals for portable navigation devices (PND) so as to affect the navigating and positioning quality such that the users may not have faith to count on the related products of global positioning system (GPS). Taking the constructions shown in FIG. 1A as an example, it illustrates a plane road 10 and an elevated highway 11, such as a viaduct, constructed parallel to the plane road 10. When a carrier is moving on the plane road 10, the elevated highway 11 will impede the satellite signals so as to reducing the communication quality for satellite positioning. In addition, when a carrier is moving on the roadway between the high buildings in a downtown area illustrated in the FIG. 1B, there are also many dead spaces influencing the reception of the satellite signals in such area. Meanwhile, taking an example when a carrier is moving inside an underground passage, the satellite signals will also be impeded as well. Therefore, for the foregoing said road features while using the GPS, the conventional navigation software with respect to the GPS will not provide a modified navigating route due to the problem of signals obstruction.
For solving the satellite signals obstruction of GPS in foregoing cases, inertial navigation system (INS) will be an alternative solution for continuing to perform the navigating and positioning function. However, as shown in FIG. 2, which is an illustration showing inaccuracy caused by the conventional inertial navigating system, a carrier 90 is expected to circle around along a roadway 12, and the real line 13 is a theoretical navigating round displayed on a screen. Since the conventional INS has a problem of accumulated error, the position of the carrier shown in the display will be deviated from the theoretical navigating road 13 after the inertial signal of INS is accumulated for a period of time. Hence, if the accumulated error of INS during the carrier moving is not modified immediately, an erroneous deviation due to the accumulated error will induce an erroneous route 14 shown on a display after the carrier is circling around the roadway 12.
The foregoing problem is common in the prior art of navigation, so the U.S. Pat. No. 5,774,824 is provided to solve the problem, wherein the technique judges error according to a measured point of the vehicle and a matched point of the vehicle on a map route defined according to a map database having a plurality of links and a plurality of nodes. If the measured point deviated from the map route, then an analyzer detects an end of a curve in the map route and updates the measured point and the matched point to the end of the curve and the modified navigating information is displayed on a display unit for guiding the driver. Owing to the foregoing method is performed base on an assumption that the carrier is impossible to deviate the route, so sticking the image representing the carrier on the map route compulsorily according to transverse deviation between the measured point associated of the vehicle and the matched point with respect to the map route can only modify the deviation of transversely but can't modify the radial deviation of the carrier and positioning information.